West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 73 near the shore to around 61 above 3000 feet. Light winds. Chance of rain 20 percent.

Monday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 86 to 91 near the shore to around 77 above 3000 feet. East winds up to 15 mph shifting to the south in the afternoon. Chance of rain 50 percent.

Monday Night: Partly cloudy. Isolated showers after midnight. Lows 71 to 76 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph in the evening becoming light. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 74. Light winds. Chance of rain 30 percent.

Monday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 83 to 91. Northeast winds up to 10 mph shifting to the east in the afternoon. Chance of rain 30 percent.

Monday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 64 to 71 in the valleys to around 60 above 4000 feet. Light winds. Chance of rain 20 percent.

Monday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 77 to 85 in the valleys to around 67 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Monday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 64 to 71 in the valleys to around 60 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 66 to 74. Light winds. Chance of rain 20 percent.

Monday: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs 79 to 88. East winds up to 15 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy in the evening, then mostly cloudy with scattered showers after midnight. Lows 66 to 74. East winds up to 10 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 65 to 78. Light winds. Chance of rain 20 percent.

Monday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 88. South winds up to 10 mph shifting to the east around 10 mph in the afternoon. Chance of rain 40 percent.

Monday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 65 to 78. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A stable, light to moderate trade wind flow will produce light rainfall over windward slopes tonight, and drier air moving in from the east on Monday will lead to a decrease in shower activity on most islands. Hurricane Kiko is forecast to pass north of the island chain on Tuesday and Wednesday, disrupting the trade winds, producing increased humidity with areas heavy rainfall, and generating large surf along east facing shores.

Discussion

Sea breezes have overpowered a weak trade wind flow today as stable conditions remain in place. Trades are suppressed as the local pressure gradient has been weakened by a trough sitting roughly 200 miles north of Kauai. The upper-level low supporting this trough weakens considerably over the islands, allowing a lingering mid-level ridge to maintain stable conditions with an inversion holding between 5,000 to 8,000 ft. A very diffuse area of low- level moisture within the weak trade wind flow managed to produce isolated modest rainfall on Maui County and Oahu today, while other areas have remained mostly dry. As this moisture pushes slowly westward overnight, expect higher chances for mainly light showers to be focused on windward Oahu and eventually Kauai.
Except for a few lingering showers near Kauai and Oahu in the morning, a slot of rather dry conditions will spread from east to west on Monday as Hurricane Kiko approaches the region. Towards sunset, moisture along the western flank of weakening Kiko will near the windward coasts of the Big Island and Maui.
The latest National Hurricane Center forecasts continue to show Kiko weakening to a tropical storm as it passes north of the islands Tuesday and Wednesday. Confidence in this scenario is increasing, though interests in Hawaii should continue to monitor official forecasts for Kiko. Moisture along the periphery of the system will spread over the state Monday night and Tuesday. Initially, this will provide an increase in clouds and mainly windward showers, but as trade winds become disrupted, afternoon sea breezes will likely trigger spotty interior rainfall. These showers could be locally heavy in places, and we cannot rule out a brief thunderstorm as the atmosphere destabilizes on Tuesday. As dew points creep into the low to mid 70s, rather humid conditions will prevail. In addition, large surf will affect east facing shores, and see the marine section of this discussion for more details.
As Kiko moves off to the northwest of the state on Wednesday night and Thursday, moderate trade winds and a ridge aloft are expected to build in from the east. The resulting stable conditions will bring a drier air mass with a typical pattern of windward rainfall and dew points dropping back into the mid 60s.

Aviation

Winds will remain rather light through tonight, with widespread land and sea breezes. Clouds and isolated showers will continue over leeward and interior areas through this evening, with some clearing overnight. Light to moderate trades expected on Monday, with localized land and sea breezes. Expect an increase in clouds and showers tomorrow afternoon as moisture associated with Tropical Cyclone Kilo starts to filter into the region. Brief MVFR is possible with any showers. Otherwise, expect mainly VFR across the state, with an increasing chance of MVFR cigs on Monday.
Tropical Cyclone Kiko will approach the Hawaiian Islands from the southeast over the next couple of days. The National Hurricane Center is currently forecasting Kiko to pass north of the islands on Tuesday. Any deviation south of this forecast track may result in wind and rain impacts to the state.
No AIRMETs are in effect nor expected through tonight. AIRMET Sierra for tempo mountain obscuration may be necessary on Monday as moisture from Tropical Cyclone Kiko moves into the area.

Marine

A weak trough north of the state will continue to drift westward and away from the state through Monday. As this trough moves away, a brief return of moderate to locally fresh trades is expected on Monday. Trades could still be light enough for localized sea breezes during the day Monday especially over the western half of the state.
Attention then turns to Hurricane Kiko, which was located approximately 550 NM E of Hilo this afternoon. Hurricane Kiko continues to track west-northwest in the Central Pacific, and according to the latest forecast from the National Hurricane Center, is expected to enter our offshore waters Monday night as a weakening Hurricane. Kiko will then continue to move west-northwest through the offshore waters as it weakens to tropical storm status. A Hurricane Warning remains in effect for the offshore waters with hurricane conditions expected over the E and NE offshore waters Monday and Monday night. As far as the coastal waters, confidence is increasing for Kiko to stay north of the coastal waters. Although no wind impacts are expected over the coastal waters, a quick rise of wave heights are expected Monday night into Tuesday as Kiko passes.
Surf along east facing shores will slowly rise through Monday as swell energy from Tropical Cyclone Kiko arrives. Latest buoy observations from Hilo and buoy 51004 show some increase in the 10 second spectral bands, but only a subtle increase in the longer periods. This suggests surf will likely come in below guidance in the near-term with surf likely staying below advisory thresholds through Monday. Although as Kiko nears the state late Monday into Tuesday, we should see a rapid increase of swell with surf heights possibly reaching low end High Surf Warning levels Monday night into Tuesday along east facing shores. The rise in surf will be short-lived with a steady decline expected Tuesday through Tuesday night. Surf will likely drop well below advisory thresholds by Wednesday. Note, peak surf heights will be highly dependent on the track and intensity of Kiko as it nears the state.
A moderate long period south-southwest swell will peak today helping to build surf above the summer average. As this swell declines on Monday, another reinforcing swell out of the south- southwest is expected on Tuesday. This should help maintain surf near or slightly above the summer average throughout the first half of the week. Additionally, multiple small pules of northwest swell energy will generate small surf along north facing beaches throughout the week.
Peak monthly high tides, combined with water levels running higher than predicted, may lead to minor flooding along the shoreline and in low lying coastal areas. A Coastal Flood Statement remains in effect through this afternoon. Coastal Flood Statement is expected to be cancelled later today.

Fire weather

Winds are forecast to remain below critical fire weather thresholds for the next few days. A narrow slot of very dry and stable air will move over the islands from east to west on the weak trade wind flow Monday. This could push the inversion down to around 4,000 feet and produce very low humidity at higher elevations of the Kaala Fire in the Hamakua District of the Big Island. Increased humidity and higher chances for rainfall are expected Monday night into Wednesday and Tropical Cyclone Kiko passes north of the state.

HFO Watches/Warnings/Advisories

None.

Kauai Now Weather is brought to you by Blue Hawaiian Helicopters.